Staff at one of Queen Elizabeth II's homes, Windsor Castle, have voted in favour of industrial action over pay, the first ever by royal staff, a trade union said Wednesday.

Wardens at Windsor Castle, which is west of London and dates back to the 11th century, look set to take action from the end of this month, the Public and Commercial Service (PCS) said.

The wardens work at the castle entrance and around the grounds as well as inside the castle, helping visitors and protecting artworks.

Their salaries can start at £14,400 a year (20,000 euros, $21,200) but the union says they are also expected to carry out additional unpaid duties such as giving tours of the castle.

"These loyal workers are the public face of Windsor Castle and with this vote their message to their employer is loud and clear," PCS general secretary Mark Serwotka said.

"Staff should be properly rewarded for their commitment to ensuring visitors from around the world can fully enjoy their time at the castle."

Queen Elizabeth II usually spends weekends at Windsor Castle and is currently in residence there for a month-long period known as Easter Court, where she hosts a series of high-profile guests.

The union represents 120 out of 200 staff at Windsor Castle and 76 of the wardens were balloted, with 84 percent voting for industrial action.